Indoor TOA Error Measurement, Modeling, and Analysis

This paper presents a comprehensive investigation on the error characteristics of time-of-arrival (TOA) measurements obtained from positioning systems in indoor environments where rich multipath and nonline-of-sight propagation exist. By careful analysis of the measured data from three different sets of measurements, a model for the range errors is developed. The model has two components, one associated with the TOA measurement in the receiver and another associated with the delay excesses accumulated along the propagation path. By modeling multipath signals mathematically, and application of the central limit theorem, it is shown that statistical shape of the leading edge of a received pulse is essentially independent of the details of the scattering environment. Application of this statistical shape of the leading edge allows estimates of the statistical distribution of the TOA measurements to be calculated, either analytically or numerically from simulations. The second component of the delay excess is a model based on the number of walls along the path. Statistical performance based on this combined model is shown to be in good agreement with measured data collected from three different systems that have different RF frequencies, signal bandwidths, and TOA detection algorithms. The insights afforded by the theory assists in the design of more accurate positioning systems.